This invention relates to the adaptation of personal computers to communication through external networks, and more particularly to the ready adaptation of such computers to networks of varying characteristics, such as telecommunications networks located in various countries of the world.
Personal computer systems in general and IBM personal computers in particular have attained widespread use for providing computer power to many segments of today's modern society. Personal computer systems can usually be defined as a desk top, floor standing, or portable microcomputer that consists of a system unit having a single system processor and associated volatile and non-volatile memory, a display monitor, a keyboard, one or more diskette drives, a fixed disk storage, and an optional printer. One of the distinguishing characteristics of these systems is the use of a motherboard or system planar to electrically connect these components together. Many of these systems are designed primarily to give independent computing power to a single user and are inexpensively priced for purchase by individuals or small businesses. Others are intended to become network servers in Local Area Networks (LANs). Examples of such personal computer systems are IBM's PERSONAL COMPUTER AT and IBM's PERSONAL SYSTEM/2 Models 25, 30, L40SX, 50, 55, 65, 70, 80, 90 and 95.
These systems can be classified into two general families. The first family, usually referred to as Family I Models, use a bus architecture exemplified by the IBM PERSONAL COMPUTER AT and other "IBM compatible" machines. The second family, referred to as Family II Models, use IBM's MICRO CHANNEL bus architecture exemplified by IBM's PERSONAL SYSTEM/2 Models 50 through 95. The Family I models typically have used the popular INTEL 8088 or 8086 microprocessor as the system processor. These processors have the ability to address one megabyte of memory. The Family II models typically use the high speed INTEL 80286, 80386, and 80486 microprocessors which can operate in a real mode to emulate the slower speed INTEL 8086 microprocessor or a protected mode which extends the addressing range from 1 megabyte to 4 Gigabytes for some models. In essence, the real mode feature of the 80286, 80386, and 80486 processors provide hardware compatibility with software written for the 8086 and 8088 microprocessors.
Personal computers of the types described have heretofore been used to communicate over a number of different types of networks external to the personal computers. By way of example, it has become common to provide a modulator/demodulator ("modem") for communication by telephone networks. Such telephone networks may be the public switched telephone network common in the country of use of the system, or may be advanced telephone networks such as an integrated services digital network ("ISDN"), or the like. Typically, communication by modem is analog communication on the network side, consistent with the voice capabilities of the telephone lines used, and digital on the computer side. It has also become common to provide for communication among personal computers by a local area network ("LAN") or other network which is not primarily directed at voice communication among persons, as is the public switched telephone network. As will be appreciated, such networks having varying characteristics, specifically including varying requirements for physical connections, signal conditioning and safety. While this is particularly true of the public switched telephone networks of various countries (many of which have adopted standards for their national telephone systems distinctive from those of other countries), the problem exists for any of the types of networks mentioned above.
Heretofore, the adaptation of a personal computer to communication over a network has been accommodated by the use of an outboard accessory, such as a modem, or the use of an option card or accessory board added within the housing of the computer which functions similarly to the outboard accessory. Such accessories have typically been adapted to a specific network (analog or digital) by design and construction, and have only limited adaptability to other networks, if any. As a consequence, attempts to adapt personal computers to networks of varying characteristics have required a large number of types of adapters. For some types of networks, there is little demand for adapters, consequently such low demand adapters become difficult to obtain or expensive.